There are two major types of active electric windows, PDLC (polymer dispersed liquid crystal) and suspended particle device (SPD).
PDLC technology requires micrometer sized liquid crystals to be scattered in an organic polymeric matrix. The optical axes of the liquid crystals (LCs) are normally in random orientations. Therefore, light is scattered to different directions due to the mismatch of refraction indexes between the LCs and the polymer matrix. This makes the electric window non-transparent. However, an electric field can be applied to control and align the optical axes of LCs in the same direction. This makes the electric window turn clear due to the index of refraction matching between LCs and polymer matrix.
A PDLC returns to random orientation, and therefore non-transparent, when the electric field is removed. The PDLC was invented by Dr. Doane and his team in 1984 and published in U.S. Pat. No. 4,688,900. The liquid crystals are made with phase separation technology. PDLCs are made by mixing water insoluble monomers, e.g. epoxy resin and curing agent, with LCs to form a transparent solution. The LC micro particles separate out and disperse in the epoxy matrix due to decreasing solubility as the curing of epoxy proceeds. Electric windows use the LC properties of being able to be oriented by electricity and being naturally random in orientation without an imposed electric field. Light cannot pass through the random LC/epoxy mixture. LCs are aligned with an electric field, which turns translucent mixture into transparent clear.
A suspended particle device (SPD) uses rod-like particles suspended in an encapsulated liquid solution. It is laminated between two sheets of glass or plastic containing transparent electrodes. Similarly to the case of the PDLC, the suspended particles are in random orientation when no electric field is applied. Light is absorbed by particles and the window becomes dark and non-transparent. On the other hand, particles align in the same direction to allow light to transmit through the SPD when electric field is applied. Electricity can be applied to the threshold to control the amount of allowable light or heat transmitted. It becomes a tool for energy saving from air-conditioning in the summer and heating in the winter. In other words, SPD windows can reduce carbon emissions and the cost of expensive glass sealing material.
The light emitting diode (LED) is a semiconducting electronic component comprising a composite light source from inorganic trivalent and pentavalent elements. The initial application of LEDs was for indicator lighting and displays. LEDs are now used in general lighting application since the invention of white light LED. In this teaching, LEDs will be integrated with electric window technology to produce a multi-purpose electric window.